Hi David,
On Wed, 5 Dec 2007 19:03:12 -0800, David Brownell wrote:
> On Friday 30 November 2007, David Brownell wrote:
> > Thanks for the review. I'll snip out typos and similar trivial
> > comments (and fix them!), using responses here for more the
> > substantive feedback.
>
> Here's the current version of this patch ... updated to put the
> driver into drivers/gpio (separate patch setting that up) and
> the header into <linux/i2c/pcf857x.h>
>
> Note that after looking at the GPIO expanders listed at the NXP
> website, I updated this to accept a few more of these chips.
> Other than reset pins and addressing options, the key difference
> between these seems to be the top I2C clock speed supported:
>
> pcf857x ... 100 KHz
> pca857x ... 400 KHz
> pca967x ... 1000 KHz
>
> Otherwise they're equivalent at the level of just swapping parts.
>
> - Dave
>
> ============= SNIP!
> This is a new-style I2C driver for most common 8 and 16 bit I2C based
> "quasi-bidirectional" GPIO expanders: pcf8574 or pcf8575, and several
> compatible models (mostly faster, supporting I2C at up to 1 MHz).
>
> Since it's a new-style driver, these devices must be configured as
> part of board-specific init. That eliminates the need for error-prone
> manual configuration of module parameters, and makes compatibility
> with legacy drivers (pcf8574.c, pc8575.c)for these chips easier.
Missing space after closing parenthesis. Also, I don't quite see what
is supposed to make compatibility with the legacy drivers easier, nor
how, not why it matters in the first place.
>
> The driver exposes the GPIO signals using the platform-neutral GPIO
> programming interface, so they are easily accessed by other kernel
> code. The lack of such a flexible kernel API is what has ensured
> the proliferation of board-specific drivers for these chips... stuff
> that rarely makes it upstream since it's so ugly. This driver will
> let them use standard calls.
>
> Signed-off-by: David Brownell <[email protected]>
> ---
> drivers/gpio/Kconfig | 23 +++
> drivers/gpio/Makefile | 2
> drivers/gpio/pcf857x.c | 331 ++++++++++++++++++++++++++++++++++++++++++++
> include/linux/i2c/pcf857x.h | 45 +++++
> 4 files changed, 401 insertions(+)
>
> --- a/drivers/gpio/Kconfig 2007-12-05 15:13:27.000000000 -0800
> +++ b/drivers/gpio/Kconfig 2007-12-05 15:14:12.000000000 -0800
> @@ -5,4 +5,27 @@
> menu "GPIO Support"
> depends on GPIO_LIB
>
> +config GPIO_PCF857X
> + tristate "PCF857x, PCA857x, and PCA967x I2C GPIO expanders"
> + depends on I2C
> + help
> + Say yes here to provide access to most "quasi-bidirectional" I2C
> + GPIO expanders used for additional digital outputs or inputs.
> + Most of these parts are from NXP, though TI is a second source for
> + some of them. Compatible models include:
> +
> + 8 bits: pcf8574, pcf8574a, pca8574, pca8574a,
> + pca9670, pca9672, pca9674, pca9674a
> +
> + 16 bits: pcf8575, pcf8575c, pca8575,
> + pca9671, pca9673, pca9675
> +
> + Your board setup code will need to declare the expanders in
> + use, and assign numbers to the GPIOs they expose. Those GPIOs
> + can then be used from drivers and other kernel code, just like
> + other GPIOs, but only accessible from task contexts.
> +
> + This driver provides an in-kernel interface to those GPIOs using
> + platform-neutral GPIO calls.
> +
> endmenu
> --- a/drivers/gpio/Makefile 2007-12-05 15:14:03.000000000 -0800
> +++ b/drivers/gpio/Makefile 2007-12-05 15:14:12.000000000 -0800
> @@ -1 +1,3 @@
> # gpio support: dedicated expander chips, etc
> +
> +obj-$(CONFIG_GPIO_PCF857X) += pcf857x.o
> --- /dev/null 1970-01-01 00:00:00.000000000 +0000
> +++ b/drivers/gpio/pcf857x.c 2007-12-05 15:15:18.000000000 -0800
> @@ -0,0 +1,331 @@
> +/*
> + * pcf857x - driver for pcf857x, pca857x, and pca967x I2C GPIO expanders
> + *
> + * Copyright (C) 2007 David Brownell
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, write to the Free Software
> + * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/slab.h>
> +#include <linux/i2c.h>
> +#include <linux/i2c/pcf857x.h>
> +
> +#include <asm/gpio.h>
> +
> +
> +/*
> + * The pcf857x, pca857x, and pca967x chips only expose one read and one
> + * write register. Writing a "one" bit (to match the reset state) lets
> + * that pin be used as an input; it's not an open-drain model, but acts
> + * a bit like one. This is described as "quasi-bidirectional"; read the
> + * chip documentation for details.
> + *
> + * Some other I2C GPIO expander chips (like the pca953{4,5,6,7,9}, pca9555,
> + * pca9698, mcp23008, and mc23017) have more complex register models with
mc_p_23017?
> + * more conventional input circuitry, often using 0x20..0x27 addresses.
> + */
> +struct pcf857x {
> + struct gpio_chip chip;
> + struct i2c_client *client;
> + unsigned out; /* software latch */
> +};
> +
> +/*-------------------------------------------------------------------------*/
> +
> +/* Talk to 8-bit I/O expander */
> +
> +static int pcf857x_input8(struct gpio_chip *chip, unsigned offset)
> +{
> + struct pcf857x *gpio = container_of(chip, struct pcf857x, chip);
> +
> + gpio->out |= (1 << offset);
> + return i2c_smbus_write_byte(gpio->client, gpio->out);
> +}
> +
> +static int pcf857x_get8(struct gpio_chip *chip, unsigned offset)
> +{
> + struct pcf857x *gpio = container_of(chip, struct pcf857x, chip);
> + s32 value;
> +
> + value = i2c_smbus_read_byte(gpio->client);
> + return (value < 0) ? 0 : (value & (1 << offset));
This is no longer a boolean value, is that OK? I guess that it doesn't
matter but maybe it should be documented (what GPIO drivers are allowed
to return in these callback functions.)
> +}
> +
> +static int pcf857x_output8(struct gpio_chip *chip, unsigned offset, int value)
> +{
> + struct pcf857x *gpio = container_of(chip, struct pcf857x, chip);
> + unsigned bit = 1 << offset;
> +
> + if (value)
> + gpio->out |= bit;
> + else
> + gpio->out &= ~bit;
> + return i2c_smbus_write_byte(gpio->client, gpio->out);
> +}
> +
> +static void pcf857x_set8(struct gpio_chip *chip, unsigned offset, int value)
> +{
> + pcf857x_output8(chip, offset, value);
> +}
> +
> +/*-------------------------------------------------------------------------*/
> +
> +/* Talk to 16-bit I/O expander */
> +
> +static int i2c_write_le16(struct i2c_client *client, u16 word)
> +{
> + u8 buf[2] = { word & 0xff, word >> 8, };
Stray comma.
> + int status;
> +
> + status = i2c_master_send(client, buf, 2);
> + return (status < 0) ? status : 0;
> +}
> +
> +static int i2c_read_le16(struct i2c_client *client)
> +{
> + u8 buf[2];
> + int status;
> +
> + status = i2c_master_recv(client, buf, 2);
> + if (status < 0)
> + return status;
> + return (buf[1] << 8) | buf[0];
> +}
> +
> +static int pcf857x_input16(struct gpio_chip *chip, unsigned offset)
> +{
> + struct pcf857x *gpio = container_of(chip, struct pcf857x, chip);
> +
> + gpio->out |= (1 << offset);
> + return i2c_write_le16(gpio->client, gpio->out);
> +}
> +
> +static int pcf857x_get16(struct gpio_chip *chip, unsigned offset)
> +{
> + struct pcf857x *gpio = container_of(chip, struct pcf857x, chip);
> + int value;
> +
> + value = i2c_read_le16(gpio->client);
> + return (value < 0) ? 0 : (value & (1 << offset));
> +}
> +
> +static int pcf857x_output16(struct gpio_chip *chip, unsigned offset, int value)
> +{
> + struct pcf857x *gpio = container_of(chip, struct pcf857x, chip);
> + unsigned bit = 1 << offset;
> +
> + if (value)
> + gpio->out |= bit;
> + else
> + gpio->out &= ~bit;
> + return i2c_write_le16(gpio->client, gpio->out);
> +}
> +
> +static void pcf857x_set16(struct gpio_chip *chip, unsigned offset, int value)
> +{
> + pcf857x_output16(chip, offset, value);
> +}
> +
> +/*-------------------------------------------------------------------------*/
> +
> +static int pcf857x_probe(struct i2c_client *client)
> +{
> + struct pcf857x_platform_data *pdata;
> + struct pcf857x *gpio;
> + int status;
> +
> + pdata = client->dev.platform_data;
> + if (!pdata)
> + return -ENODEV;
> +
> + /* Allocate, initialize, and register this gpio_chip. */
> + gpio = kzalloc(sizeof *gpio, GFP_KERNEL);
> + if (!gpio)
> + return -ENOMEM;
> +
> + gpio->chip.base = pdata->gpio_base;
> + gpio->chip.can_sleep = 1;
> +
> + /* NOTE: the OnSemi jlc1562b is also largely compatible with
> + * these parts, notably for output. It has a low-resolution
> + * DAC instead of pin change IRQs; and its inputs can be the
> + * result of comparators.
> + */
> +
> + /* 8574 addresses are 0x20..0x27; 8574a uses 0x38..0x3f;
> + * 9670, 9672, 9764, and 9764a use quite a variety.
> + *
> + * NOTE: we dont distinguish here between *4 and *4a parts.
Typo: don't.
> + */
> + if (strcmp(client->name, "pcf8574") == 0
> + || strcmp(client->name, "pca8574") == 0
> + || strcmp(client->name, "pca9670") == 0
> + || strcmp(client->name, "pca9672") == 0
> + || strcmp(client->name, "pca9674") == 0
> + ) {
> + gpio->chip.ngpio = 8;
> + gpio->chip.direction_input = pcf857x_input8;
> + gpio->chip.get = pcf857x_get8;
> + gpio->chip.direction_output = pcf857x_output8;
> + gpio->chip.set = pcf857x_set8;
> +
> + if (!i2c_check_functionality(client->adapter,
> + I2C_FUNC_SMBUS_BYTE))
> + status = -EIO;
> +
> + /* fail if there's no chip present */
> + else
> + status = i2c_smbus_read_byte(client);
> +
> + /* '75/'75c addresses are 0x20..0x27, just like the '74;
> + * the '75c doesn't have a current source pulling high.
> + * 9671, 9673, and 9765 use quite a variety of addresses.
> + *
> + * NOTE: we dont distinguish here between 8575/8575a parts.
> + */
> + } else if (strcmp(client->name, "pcf8575") == 0
> + || strcmp(client->name, "pca8575") == 0
> + || strcmp(client->name, "pca9671") == 0
> + || strcmp(client->name, "pca9673") == 0
> + || strcmp(client->name, "pca9675") == 0
> + ) {
> + gpio->chip.ngpio = 16;
> + gpio->chip.direction_input = pcf857x_input16;
> + gpio->chip.get = pcf857x_get16;
> + gpio->chip.direction_output = pcf857x_output16;
> + gpio->chip.set = pcf857x_set16;
> +
> + if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
> + status = -EIO;
> +
> + /* fail if there's no chip present */
> + else
> + status = i2c_read_le16(client);
> +
> + } else
> + status = -ENODEV;
> +
> + if (status < 0)
> + goto fail;
> +
> + gpio->chip.label = client->name;
> +
> + gpio->client = client;
> + i2c_set_clientdata(client, gpio);
> +
> + /* NOTE: these chips have strange "quasi-bidirectional" I/O pins.
> + * We can't actually know whether a pin is configured (a) as output
> + * and driving the signal low, or (b) as input and reporting a low
> + * value ... without knowing the last value written since the chip
> + * came out of reset (if any). We can't read the latched output.
> + *
> + * In short, the only reliable solution for setting up pin direction
> + * is to do it explicitly. The setup() method can do that.
> + *
> + * We use pdata->n_latch to avoid trouble. In the typical case it's
> + * left initialized to zero; our software copy of the "latch" then
> + * matches the chip's all-ones reset state. But some systems will
> + * need to drive some pins low, while avoiding transient glitches.
> + * Handle those cases by assigning n_latch to a nonzero value.
> + */
> + gpio->out = ~pdata->n_latch;
> +
> + status = gpiochip_add(&gpio->chip);
> + if (status < 0)
> + goto fail;
> +
> + /* NOTE: these chips can issue "some pin-changed" IRQs, which we
> + * don't yet even try to use. Among other issues, the relevant
> + * genirq state isn't available to modular drivers; and most irq
> + * methods can't be called from sleeping contexts.
> + */
> +
> + dev_info(&client->dev, "gpios %d..%d on a %s%s\n",
> + gpio->chip.base,
> + gpio->chip.base + gpio->chip.ngpio - 1,
> + client->name,
> + client->irq ? " (irq ignored)" : "");
> +
> + /* Let platform code set up the GPIOs and their users.
> + * Now is the first time anyone can use them.
> + */
> + if (pdata->setup) {
> + status = pdata->setup(client,
> + gpio->chip.base, gpio->chip.ngpio,
> + pdata->context);
> + if (status < 0)
> + dev_err(&client->dev, "%s --> %d\n",
> + "setup", status);
Shouldn't this be degraded to dev_warn? The probe still succeeds. Or
keep dev_err but make the probe fail (in which case you'll probably
want to swap this block of code with the dev_info above.)
> + }
> +
> + return 0;
> +
> +fail:
> + dev_dbg(&client->dev, "probe error %d for '%s'\n",
> + status, client->name);
> + kfree(gpio);
> + return status;
> +}
> +
> +static int pcf857x_remove(struct i2c_client *client)
> +{
> + struct pcf857x_platform_data *pdata = client->dev.platform_data;
> + struct pcf857x *gpio = i2c_get_clientdata(client);
> + int status = 0;
> +
> + if (pdata->teardown) {
> + status = pdata->teardown(client,
> + gpio->chip.base, gpio->chip.ngpio,
> + pdata->context);
> + if (status < 0) {
> + dev_err(&client->dev, "%s --> %d\n",
> + "teardown", status);
> + return status;
> + }
> + }
> +
> + status = gpiochip_remove(&gpio->chip);
> + if (status == 0)
> + kfree(gpio);
> + else
> + dev_err(&client->dev, "%s --> %d\n", "remove", status);
> + return status;
> +}
> +
> +static struct i2c_driver pcf857x_driver = {
> + .driver = {
> + .name = "pcf857x",
> + .owner = THIS_MODULE,
> + },
> + .probe = pcf857x_probe,
> + .remove = pcf857x_remove,
> +};
> +
> +static int __init pcf857x_init(void)
> +{
> + return i2c_add_driver(&pcf857x_driver);
> +}
> +/* we want GPIOs to be ready at device_initcall() time */
> +subsys_initcall(pcf857x_init);
> +
> +static void __exit pcf857x_exit(void)
> +{
> + i2c_del_driver(&pcf857x_driver);
> +}
> +module_exit(pcf857x_exit);
> +
> +MODULE_LICENSE("GPL");
> +MODULE_AUTHOR("David Brownell");
> --- /dev/null 1970-01-01 00:00:00.000000000 +0000
> +++ b/include/linux/i2c/pcf857x.h 2007-12-05 15:14:12.000000000 -0800
> @@ -0,0 +1,45 @@
> +#ifndef __LINUX_PCF857X_H
> +#define __LINUX_PCF857X_H
> +
> +/**
> + * struct pcf857x_platform_data - data to set up pcf857x driver
> + * @gpio_base: number of the chip's first GPIO
> + * @n_latch: optional bit-inverse of initial register value; if
> + * you leave this initialized to zero the driver will act
> + * like the chip was just reset
> + * @setup: optional callback issued once the GPIOs are valid
> + * @teardown: optional callback issued before the GPIOs are invalidated
> + * @context: optional parameter passed to setup() and teardown()
> + *
> + * In addition to the I2C_BOARD_INFO() state appropriate to each chip,
> + * the i2c_board_info used with the pcf875x driver must provide the
> + * chip "type" ("pcf8574", "pcf8574a", "pcf8575", "pcf8575c") and its
> + * platform_data (pointer to one of these structures) with at least
> + * the gpio_base value initialized.
> + *
> + * The @setup callback may be used with the kind of board-specific glue
> + * which hands the (now-valid) GPIOs to other drivers, or which puts
> + * devices in their initial states using these GPIOs.
> + *
> + * These GPIO chips are only "quasi-bidirectional"; read the chip specs
> + * to understand the behavior. They don't have separate registers to
> + * record which pins are used for input or output, record which output
> + * values are driven, or provide access to input values. That must be
> + * inferred by reading the chip's value and knowing the last value written
> + * to it. If you leave n_latch initialized to zero, that last written
> + * value is presumed to be all ones (as if the chip were just reset).
> + */
> +struct pcf857x_platform_data {
> + unsigned gpio_base;
> + unsigned n_latch;
> +
> + int (*setup)(struct i2c_client *client,
> + int gpio, unsigned ngpio,
> + void *context);
> + int (*teardown)(struct i2c_client *client,
> + int gpio, unsigned ngpio,
> + void *context);
> + void *context;
> +};
> +
> +#endif /* __LINUX_PCF857X_H */
The rest looks fine to me.
--
Jean Delvare
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